Loudspeakers used in audio systems are often electrodynamic speakers. Electrodynamic speakers typically have a magnetic motor which moves a cone-shaped diaphragm, thereby creating pressure waves in the surround air, and thus causing sound. The cone-shaped diaphragm is situated within a frame, or a basket, with a wide end of the cone coupled to the frame by way of a flexible membrane, called a suspension, or a surround. The flexible membrane axially centers the cone-shaped diaphragm within the frame, while allowing the cone-shaped diaphragm to move back and forth at audio frequencies. A narrow end of the cone-shaped diaphragm is coupled to the frame by another flexible membrane, called a spider, which also helps to axially center the moving diaphragm.
The motor generally has a voice coil, which usually is behind the narrow end of the cone-shaped diaphragm, and a magnetic circuit adjacent to and/or partially surrounding the voice coil. In operation, electrical audio signals from an amplifier, or other suitable source, are applied to the voice coil, producing a varying electromagnetic field, which interacts with a magnetic field of the magnetic circuit. Interaction between the magnetic fields causes the voice coil to move and, in turn, causes the cone-shaped diaphragm to move in and out relative to the frame. The motion of the diaphragm is why the diaphragm and voice coil are often referred to as a piston, or a driver. The moving diaphragm and voice coil causes pressure waves in the air around the speaker, thereby producing audible sound. Speakers generally are mounted within enclosures to prevent sounds waves emitted from the rear of the diaphragm from interfering with sound waves emitted from the front of the diaphragm.
Speakers typically are divided into three categories: woofer, midrange, and tweeter. A woofer produces low frequency sound ranging from about 20 Hz to 3000 Hz. A midrange speaker produces a broad spectrum of sound, typically ranging between about 1000 Hz and 10 kHz. A tweeter speaker produces high frequency sound ranging between about 4 kHz and 20 kHz. Home audio systems often have a woofer, a midrange, and a tweeter housed within a single enclosure, as in the case of free-standing or floor speaker configurations. Where space is a consideration, the functions of the woofer and midrange may be combined into a single speaker, as in the case of bookshelf-sized speaker configurations.
A drawback to conventional speakers used with home audio systems is a lack of portability. Speaker systems that are housed within enclosures typically are heavy and often bulky, and thus are not amenable to being moved from room to room. Further, speakers that operate with computers typically are cumbersome and have various cables attached, making portability inconvenient. Another drawback is that conventional speakers have fixed frequency ranges. Thus, for example, a woofer speaker generally cannot adjust the output frequency range to accommodate an audio system lacking a midrange speaker. The limitation of frequency ranges often requires at least three or more speakers to cover the audible frequency range. Still another drawback is that conventional home audio systems are not modular, and thus the various component speakers are not interchangeable, and generally are not suited for rearrangement by an end-user of the system. Conventional audio systems generally are assembled into configurations that are fixed by the manufacturer. For example, a conventional two-way audio system with a midrange speaker and a tweeter speaker both housed within an enclosure typically cannot accommodate a woofer speaker unless the user provides an entirely new enclosure suitable for housing all three speakers.